1. Technical Field
This disclosure relates generally to wireless communications, and more particularly to multiple-input multiple-output (MIMO) systems, architectures and techniques.
2. Description of Related Art
The enormous success of advanced wireless devices is pushing the demand for higher wireless data rates. Denser spectrum reuse through the deployment of more access points per square mile has the potential to successfully meet the increasing demand for more bandwidth.
In theory, the best approach to density increase is via distributed multiuser multiple-input multiple-output (MIMO) architectures and techniques, such as supported by the IEEE 802.11n standard, where several access points are connected to a central server and operate as a large distributed multi-antenna access point, ensuring that all transmitted signal power serves the purpose of data transmission, rather than creating “interference.” In practice, while enterprise networks offer a natural setup in which distributed MIMO might be possible, there are serious implementation difficulties, the primary one being the need to eliminate phase and timing offsets between the jointly coordinated access points.
However, distributed multiuser MIMO is regarded today mostly as a theoretical solution because of some serious implementation hurdles, such as the ability to eliminate phase and timing offsets between jointly coordinated access points and the ability to perform efficient joint encoding at a central server linked to the access points through wired links of limited capacity.
FIG. 1 depicts a diagram of an Enterprise Wifi and Distributed MIMO network. The network 100 includes a number of access point (or, transmitters) 102-1 and 102-2 transmitting to a number of clients (or, receivers) 104-1 through 104-3. The transmitters typically have wired links, e.g., by an Ethernet, to a central server 106. The multiple access points coordinate their transmissions to several clients by using distributed MIMO. Since in such networks the wired links connecting the access points are typically fast enough to allow for efficient joint processing at a server, the major obstacle to achieve the full potential of distributed MIMO gains has been eliminating the phase offsets between the different access points. The perceived difficulty of this task has led some researchers to believe that it is practically impossible to achieve full spatial multiplexing in the context of distributed MIMO.